<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // 更新变量
    let age = 18;
    age = 19;
    console.log(age);

    // 声明多个变量(不推荐，建议一行声明一个变量)
    let uname = 'caiwan',
      uno = 221240330;
    document.write(uname, uno);


    // testdemo

    let nname = prompt('请输入姓名：');

    document.write('</br>' + nname);
  </script>
</body>

</html>